1. Field of the Invention
This invention concerns the manufacture of laminated panes of the type known as asymmetric, composed of a monolithic or laminated rigid support and of a sheet of flexible plastic material having the desired properties, such as energy-absorber properties, surface properties such as scratch resistance, abrasion resistance and so on.
2. Discussion of the Background
Asymmetric panes composed of a monolithic or laminated rigid support and a flexible sheet of plastic material, such as at least one film of polyurethane, may be used as vehicle panes, notably as windscreens, lateral panes or rear windows for automobile vehicles; as panes for aircraft cockpits; as panes for trains or as panes of buildings and ships.
The assembling of the rigid support with the flexible sheet to form the laminated pane is generally performed by a preliminary pressing together of the support and the sheet by calendering, followed by an autoclave cycle using temperature and pressure which improves the bond between the constituent elements and thus assures the final assembling together.
There has already been proposed, in European Patent Publication 0 015 209, a calendering device comprising lower pressing elements, such as a series of small rollers or wheels disposed alongside one another, and upper pressing elements comprising a flexible cylindrical pressing roller extending over a length at least equal to the width of the elements to be assembled. The flexible roller is held to the desired curvature by upper members bearing upon it and the entire assembly of the pressing elements is mounted upon a pivoting frame.
The flexible sheet which is assembled with the rigid support by the use of this device must be in the form of a continuous band or ribbon so that it can be held in the desired position for assembly, which is carried out as the components move past.
Unfortunately, in this type of assembling with the components in motion, it is not possible to present the rigid supports for assembly, one after another and without gaps between them, especially in the case of panes curved in the direction of travel, which generally corresponds to the curvature along the length of the pane. The pivoting frame is therefore progressively tilted as the pane advances between the pressing elements, in order to ensure a pressing action substantially perpendicular to the surface of the pane throughout the entire operation.
The position of the pivoting frame as a pane departs therefrom is generally symmetrical, about a vertical plane, with the position of the pivoting frame as a pane enters therein, which means that between the departure of one pane and the entry of the next pane the frame must tilt in the reverse direction in order to return to its initial position for the start of assembly.
It is therefore necessary to separate two consecutive rigid supports by a gap at least equal to the distance corresponding to the advance of the panes during the time for tilting back of the frame. This interval therefore corresponds to a loss of flexible sheet material.
Furthermore, in the case of automobile panes, the developed surface of the pane has an approximately trapezoidal shape, which leads to other losses of flexible sheet material, in particular the entire part contained between the contours of the trapezium, which is termed the blank sheet, and the rectangle within which the blank sheet is inscribed. The various losses of material may in total amount to approximately 30% of the area of the sheet.
In Publication EP-A-0 403 321, a method has been proposed for the assembly of asymmetric panes composed of a rigid support and a flexible sheet, starting from a continuous ribbon or band, which greatly reduces the wastage of flexible sheet material.
According to this process, there is presented to the assembling device a continuous band formed of a flexible support film of paper or of an inexpensive plastic material, on which there have been placed blank sheets prepared or cut out in advance to the desired geometrical shape, these blank sheets being arranged uniformly and separated from one another. In general, the separation distance between two blank sheets is at least equal to that corresponding to the advance of the film during the period taken by the assembling device for passing from the discharge position for a pane to the entry position for the next pane.
The time taken by the device for changing position corresponds to the time for return pivoting when the device is equipped with a tilting frame.
For forming this prefabricated flexible band or ribbon, several variants are envisaged. In a first embodiment, the sheet of plastic material may be produced by format, using as a shaping support a continuous bed composed of trapeziums disposed head-to-tail. When the sheet of plastic material is removed from the shaping support, the trapezoidal blank sheets are directly obtained. These are then placed uniformly and with a single orientation on the support film to form the prefabricated band, which will be used for the later assembly by calendering.
In a variant, the flexible sheet is produced by using a continuous shaping support of glass or of metal, as described for example in French Patent Publications 2 230 487 or 2 549 414, or on a tensioned flexible support as described for example in French Patent Publication 2 480 669. The sheet of continuous plastic material produced in this manner is cut into blanks after having been pulled off the shaping support or cut out together with the support itself when the latter is a tensioned flexible support and forms part of the manufactured sheet, which is then a composite sheet. The blanks obtained are then disposed as before in a uniform manner and in a single orientation on the support film in order to form the prefabricated band which will be used for assembly.
The process described above thus enables the losses of material to be limited. It does, however, require the production in advance of a continuous band from a flexible support film and cut-out blanks. After assembly, the support film is generally lost to the process.